Radiation and Atomic Structure of Helium

Study Notes

Energy transmission occurs via particles or waves.
Ionizing radiation includes X-rays, Bremsstrahlung, characteristic X-rays, gamma radiation, annihilation radiation, positrons, electrons, protons, neutrons, alpha particles, and other heavy ions.

Helium's subatomic structure consists of 2 protons, 2 neutrons, and 2 electrons.
Protons have a large positive charge and mass, defining the element.
Neutrons have similar mass to protons but no charge.
Electrons are significantly lighter than protons and have a negative charge. Electrons orbit the nucleus.

Alpha particles are identical to helium-4 nuclei, comprising two protons and two neutrons.
Alpha radiation is often produced during alpha decay.
They can also be written as He²⁺ (identifying the loss of two electrons).
In their environment, alpha particles gain electrons, becoming electrically neutral helium atoms.

Gamma radiation is electromagnetic radiation.
Gamma rays have higher energy and shorter wavelength than X-rays; frequencies above 10¹⁹ Hz.
These energies are greater than 100 keV, and shorter wavelengths than the diameter of an atom.

X-rays have low energy (120 eV to 120 keV)
They have shorter wavelengths than ultraviolet, and longer than gamma rays.
They are also called Röntgen radiation, after Wilhelm Conrad Röntgen.
X-ray production in a tube involves high voltage to accelerate electrons toward a target.
The higher the target atom number, the higher the X-ray yield and the higher the incident electron energy results in increased X-ray production probability.
X-ray production decreases with increasing X-ray energy.

Neutron radiation is a stream of free neutrons.
Neutrons react with nuclei of other atoms; resulting in the formation of new isotopes and chain reactions.
Neutron radiation can result in nuclear fission or fusion.
This radiation is dangerous and harmful over large areas.
Neutron properties include composition (two down quarks, one up quark), rest mass, energy equivalent, an electric charge of zero, and a half-life.
Decay schemes of their radioactive decay is described.

Different neutron sources generate neutrons through various methods:
Californium-252 sources: Generate neutrons via alpha decay and fission.
(α, n) sources: Mix a source like Ra-226 with light elements like Be.
(γ,n) sources: Mix a higher-energy gamma source with light elements.
Neutron Generator: Accelerate particles to generate neutrons ( D-D and D-T reactions).
Specific sources have varying half-lives, neutron energies, and fluence rates (commonly expressed in n/cm²/s).

Neutron emission rates for alpha, gamma, and spontaneous fission neutron sources are measureable through the manganese sulfate bath technique.
The resulting neutron emission rate is calculated through gamma spectrometry of the Mn-56 product.
Detecting neutron leakage improves emissions calculations.

AmBe, PuBe, and RaBe sources comprise specific mixes of radioactive isotopes and materials.
These sources showcase characteristics such as yield, half-life, average neutron energies, and associated gamma dose rate and neutron dose rate measurements.

Beryllium is the most common low-Z material, and other materials like fluorine, lithium, and boron are alternatives to beryllium.
These alternatives have different neutron energies.

Alpha emitters and beryllium materials are intimately mixed (alpha emitter oxide + beryllium metals) and compressed into cylindrical shapes for encapsulation.
Double encapsulation with stainless steel is common to contain the source well.

Sources have high gamma activity, and neutrons are close to being monoenergetic.
The primary disadvantage is the high gamma emission rate. Gamma-emitting core surrounded by the target material.
Examples include antimony-beryllium sources, with an antimony core activated in a reactor.